There are two separate issues I saw when I was in the UK, neither of which was helpful:
1) No government subsidy for airports. Therefore there IS a landing fee (say £15-25) to cover costs and to ensure the airport remains profitable.
2) Airports that support commercial flights who cannot care less about GA. Their objective is to maximize returns for investors and GA is not one of such flights. They may be busy at certain times of the day but not busy enough. They have handling fees and minimum landing fees which brings the total to about £75-£250 per landing/parking.
If GA thinks of boycotting an airport that charges £15-£25, think again. These airports are run for GA and run on moderate means. Not going there means the airport will likely close down and disappear for good.
If GA thinks of boycotting an airport that charges £75-£200. think again. The numbers of movements are small and the income earned from it is small. You achieve nothing other than to completely lose an airport that you have access to. The airport bosses will see this as a win for them, thus paving way for their fees to go up further. You've now given up the airport to market its business to other heavier, higher-revenue traffic. You are better off at an organized campaign to government/airport bosses to bring charges to more realistic levels.
The bottom line is that GA needs basic transport infrastructure to connect people and places. And boycotting is not the way to do it.